I had no idea what a circulator was or what purpose it served. The wikipedia link has a good description of what it is, and the pdf link is a paper about how to achieve full duplex radio operation, and shows where the circulator fits into the picture.

1. https://en.wikipedia.org/wiki/Circulator

2. http://web.stanford.edu/~skatti/pubs/sigcomm13-fullduplex.pd...